Fastener driving tool

ABSTRACT

A pneumatic stapler includes a housing in which is mounted for limited sliding movement a drive cylinder containing a piston coupled to a driver blade. A nosepiece structure on the housing contains a drive track slidably receiving the blade and supporting an annular or cylindrical member aligned with the lower end of the cylinder and carrying a valve seat. A main valve engages the top of the cylinder and forces the cylinder downwardly to seat on the valve seat in the normal condition of the tool. When the main valve moves upwardly, it closes an upper cylinder exhaust valve, and the cylinder follows through its limited travel to move out of engagement with the valve seat and exhausts the lower end of the drive cylinder. Further upward movement of the main valve admits compressed air to move the drive piston downwardly through a power stroke. A cycle valve receiving air from the cylinder at the end of the power stroke controls the main valve to move downwardly and not only seat the cylinder lower end on the valve seat, but also exhaust the upper end of the cylinder interior. A return valve senses this condition and supplies compressed air through the nosepiece within the annular member to return the drive piston and to supply compressed air to the cycle valve to prevent a premature opening of the main valve. The completion of the return stroke of the piston releases the return valve. A magazine includes a biased staple strip pusher with a pair of rigid legs pivoting in the planes of the staple legs to facilitate loading the staple strips.

United States Patent [191 Novak et a1.

[ FASTENER DRIVING TOOL [75] lnventors: Raymond F. Novak, Schiller Park;

Howard B. Ramspecl-t, Chicago; Bernard W. Geist, Melrose Park; Frank R.Potucek, Des Plaines, all

[731 Assignee: Duo-Fast Corporation, Franklin Park, 111.

[22] Filed: Sept. 13, 1973 21 1 Appl. No.1 396,878

Primary Examiner-Granville Y. Custer, Jr. Allurm'y, Agent, orFirm-Mason, Kolehmainen, Rathburn & Wyss [57] ABSTRACT A pneumaticstapler includes a housing in which is [451 Sept. 16, 1975 mounted forlimited sliding movement a drive cylinder containing a piston coupled toa driver blade. A nosepiece structure on the housing contains a drivetrack slidably receiving the blade and supporting an annular orcylindrical member aligned with the lower end of the cylinder andcarrying a valve seat. A main valve engages the top of the cylinder andforces the cylinder downwardly to seat on the valve seat in the normalcondition of the tool. When the main valve moves upwardly, it closes anupper cylinder exhaust valve, and the cylinder follows through itslimited travel to move out of engagement with the valve seat andexhausts the lower end of the drive cylinder. Further upward movement ofthe main valve admits compressed air to move the drive piston downwardlythrough a power stroke. A cycle valve receiving air from the cylinder atthe end of the power stroke controls the main valve to move downwardlyand not only seat the cylinder lower end on the valve seat, but alsoexhaust the upper end of the cylinder interior. A return valve sensesthis condition and supplies compressed air through the nosepiece withinthe annular member to return the drive piston and to supply compressedair to the cycle valve to prevent a premature opening of the main valve.The completion of the return stroke of the piston releases the returnvalve. A magazine includes a biased staple strip pusher with a pair ofrigid legs pivoting in the planes of the staple legs to facilitateloading the staple strips.

16 Claims, 13 Drawing Figures PATENHQ SEP 1 6 i9?5 seam 1 0 7 mm QR $6NQN J TQM mm mm Wmw mm v9 1% mm mm m\ wGm Y mm m m mm m mm mm mm Qm N QmWNN PATENTEQ SEP 1 61975 SHEET 5 BF RWDTIXW WE? mm FASTENER DRIVING TOOLThis invention relates to a fastener driving tool and, moreparticularly, to a fastener driving tool including new and improvedfastener driving and feeding means.

There is a growing tendency to extend the applications in which powerdriven fasteners, such as staples and nails, are used. This extensionfrequently involves driving fasteners of larger sizes with the resultthat the power required of the driving tools must be increased. However,this increase in driving power must be obtained within the limitsimposed by the pressures and quantities of compressed air available inmost manufacturing and fabricating locations and by weight that can beconveniently manipulated by an operator. In general, this requires thedesign of more efficient tools. tools that are more efficient in theutilization of power available from existing compressed air sources, andtools that are more efficient in the quantity of air consumed. Includedin any consideration of the efficiency of use by the operator are theease of replenishing the supply of fasteners and, in the case ofmultifire tools, the assurance by the operator that a fastener will bedriven in each successive power stroke of the tool.

Accordingly, one object of the present invention is to provide a new andimproved fastener driving too].

A further object is to provide a fastener driving tool including a newand improved drive system.

A further object is to provide a fastener driving tool including a newand improved piston drive and return system.

A further object is to provide a fastener driving tool including ashiftable cylinder for venting the lower end of the cylinder prior tothe power stroke of a drive piston and new and improved means foreffecting the return of the drive piston.

A further object is to provide a fastener driving tool using a cyclevalve for effecting an automatic sequence of power and return strokesand a controlled source of pressurized fluid for insuring that eachreturn stroke is completed before the initiation of the following powerstroke.

A further object is to provide a fastener driving tool including a newand improved magazine for feeding fasteners to a drive track.

In accordance with these and many other objects, an embodiment of thepresent invention includes a pneumatic fastener or staple driving orapplying tool having a housing containing a drive cylinder mounted forlimited vertical reciprocation. A main valve movable into and out ofengagement with the upper end of the cylinder normally holds the lowerend of the cylinder seated on a cylindrical member upstanding from thehousing at its lower end to close off communication between the cylinderand the atmosphere. When the main valve is elevated, the cylinder moveswith the main valve through its limited travel so that the uppercylinder exhaust valve is first closed and the lower end of the cylindermoves out of engagement with the valve seat defined by the cylindricalmember, thereby connecting the lower interior of the cylinder to theatmosphere. 'Ihe main valve then moves out of engagement with the top ofthe cylinder to admit compressed air for driving a piston slidablymounted in the cylinder and a connected driver blade through a powerstroke.

A cycle valve assembly senses the arrival of the piston at the end ofits power stroke and controls a cycle (all valve in the control valveassembly to effect reclosure of the main valve. Closure of the mainvalve moves the cylinder downwardly so that its lower end seats on thecylindrical valve seat and closes off communication between theatmosphere and the lower interior of the cylinder. This movement of themain valve also vents the upper interior of the cylinder which isdetected by a return valve assembly. The return valve assembly suppliescompressed air to the lower interior of the cylinder beneath the pistonthrough a system of passageways extending to a point inside of thecylindrical lower valve. This compressed air elevates the piston to itsnormal position and also provides a supplemental signal or bias forretaining the cycle valve in its prior position. When the drive pistonreturns to its normal position, this condition is sensed by the returnvalve, and the supply of pressurized fluid below the piston isterminated to terminate one cycle of operation of the tool. When thepressurized fluid beneath the drive piston and the cycle valve leaks tothe atmosphere, the cycle valve returns to its alternate state, and anadditional cycle of operation of the tool is initiated.

A magazine assembly is provided for feeding successive staples into thedrive track in the nosepiece structure beneath the driver blade. Thismagazine assembly includes a resiliently biased pusher having a pair ofrigid arms pivotally mounted in the planes of the staple legs. Whenstaple strips are inserted into the magazine behind the pusher, rearwardmovement of the pusher pivots the legs upwardly to a position clearingtheir crowns from which they are returned to a position engaging thelegs of the last staple in the strip by a resilient bias.

Many other objects and advantages of the present invention will becomeapparent from considering the following detailed description inconjunction with the drawings in which:

FIG. 1 is a side elevational view of a pneumatically operated fastenerdriving tool embodying the present invention;

FIG. 2 is an end elevational view of the tool shown in FIG. 1;

FIG. 3 is an enlarged fragmentary sectional view taken along line 3-3 inFIG. 2;

FIG. 4 is a sectional view taken along line 44 in FIG. 3;

FIG. 5 is a fragmentary sectional view similar to FIG. 3 illustratingthe tool after the opening of a main valve assembly but prior to theinitiation of a power stroke of the tool;

FIG. 6 is an exploded perspective view of a structure for closing thelower end ofa drive cylinder in the tool;

FIG. 7 is a fragmentary sectional view illustrating the tool at the endof a power stroke and portions of the magazine assembly;

FIG. 8 is a sectional view taken along line 8-8 in FIG. 7;

FIG. 9 is a sectional view taken along line 99 in FIG. 7'.

FIG. I0 is an enlarged fragmentary sectional view taken in the directionof line l0 10 in FIG. 8;

FIG. II is a sectional view of a control valve assembly for the toolshown in a normal state;

FIG. I2 is a sectional view similar to FIG. ll illustrating the controlvalve assembly at the conclusion of a power stroke of the tool; and

FIG. 13 is a schematic diagram illustrating the control functionsperformed by the control valve assembly shown in FIGS. 11 and 12.

Referring now more specifically to FIGS. 1-3 of the drawings, therein isillustrated a fastener driving tool which is indicated generally as 20and which embodies the present invention. The tool 20 includes a housingshown generally as 22 including a vertically extending forward headportion 22A and a rearwardly extending hollow handle portion 22B. Thecavity defined by the head portion 22A and the hollow handle portion 228provide a reservoir 24 of pressurized fluid or compressed air foroperating the tool 20. Slidably mounted within the head portion 22A forlimited movement is a drive cylinder 26 normally engaged at its upperend by a main valve assembly indicated generally as 28 for selectivelyconnecting the upper interior of the cylinder 26 to the atmosphere or tothe pressurized fluid in the reservoir 24. A lower cylinder exhaustvalve assembly indicated generally as 30 selectively connects the lowerinterior of the cylinder 26 to the atmosphere prior to and during thepower stroke to improve the efi'iciency of drive of the tool 20. Apiston 32 slidably mounted within the cylinder 26 is secured to theupper end of a fastener driving blade or element 34, the lower end ofwhich is slidably received within a drive track 36 formed in a nosepieceassembly indicated generally as 38. On each power stroke of the piston32, the driver blade 34 engages and drives a staple 40 supplied to thedrive track 36 by a magazine assembly indicated generally as 42. Thepower and return strokes of the piston 32 are controlled by a controlvalve assembly indicated generally as 44.

Nosepiece Assembly 38 and Magazine 42 The magazine assembly 42 issecured at its forward end to and supported by the nosepiece assembly 38and feeds successive staples 40 from a strip thereof into the drivetrack 36 defined by the nosepiece assembly 38. This assembly alsoincludes a quick release assembly indicated generally as 46 (FIG. 1) forobtaining access to the drive track 36.

The nosepiece assembly 38 is carried out on a laminated plate assemblyindicated generally as 48 which closes the lower open end of the headportion 22A of the housing and which is secured thereto by a pluralityof nuts 50 threaded on inserts 52, the upper ends of which are threadedwithin tapped openings 54 (FIG. 6) at the lower end of the head portion22A. A nose insert 56 (FIGS. 1-3 and is disposed within aligned openings58 (FIG. 6) in the plate assembly 48 and welded thereto. The rear wallof the nose insert 56 provides the front wall of the upper portion ofthe drive track 36.

The nosepiece assembly 38 further includes a multiplate or welded,laminated, and generally T-shaped structure 60 including depending sidewalls 60A and spaced transverse cross members 608 which are secured toand are on opposite sides of the nose insert 56 by suitable fasteners62, such as a bolt carrying a nut. A shear block 64 (FIG. 3) is securedbetween depending leg portions 60A of the structure 60 and defines asubstantial portion of the back wall of the drive track 36 as well asdefining a generally U-shaped opening through which the staples 40 passinto the drive track 36.

A substantial portion of the front wall of the drive track 36 is definedby the assembly 46. This assembly includes a removable front plate 66fitting within the recess defined between the spaced depending legs A ofthe structure 60 with longitudinally extending flanged edges overlyingthe front walls of the legs 60A. The rear wall surface of the plate 66is recessed in accordance with the desired configuration of the drivetrack 36.

To provide means for detachably mounting the front plate 66 on thenosepiece assembly 38, there is provided a generally U-shaped bail 68(FIGS. 1 and 2), a bight portion 68A of which passes around the frontwall of the nosepiece structure 38 to be received within an indentation66A in the front wall of the plate 66. The free ends of the rearwardlyextending legs 68B of the bail 68 are slidably received within twoangled and elongated slots 70 formed in a lever 72. The lever 72 ispivotally mounted on a rearwardly extending portion of the shear block64 by a pivot pin 74 which passes through an elongated opening 76 in thelower rearwardly disposed portion of the shear block 64 adjacent aresilient body 77 (FIGS. 3 and 5 The bail 68 and the lever 72 provide anover-center linkage for clamping the front plate 66 in its desiredposition. When the plate 66 is to be removed, the lever 72 is pivotedabout the pivot pin 74 in a clockwise direction (FIG. I) to displace thebail 68 sufficiently to permit the plate 66 to be removed. When theplate 66 has been reassembled following, for example, the removal of ajammed staple from the drive track 36, the bight portion 68A of the bail68 is placed in the recess 66A, and the lever 72 is pivoted in acounterclockwise direction to the position shown in FIG. 1.

The magazine assembly 42 comprises a generally U- shaped magazinehousing indicated generally as 80 which is open at its top and closed atits bottom by a bottom wall 80A (FIG. 4) to define a narrow recessapproximately the size of a strip of staples 40. At its forward end, thelower wall 80A of the housing 80 is secured, as by a plurality ofmachine screws 82, to a rearwardly extending portion of the shear block64 (FIGS. 3 and 4). At its upper end. the magazine is secured to andwithin the outer lamina of the cross pieces 60B of the nosepiecestructure 60 by a plurality of machine screws 84 (FIG. 4).

To provide means for slidably supporting a strip of staples 40 withinthe cavity in the housing 80, there is provided a staple rail 86 whichis generally U-shaped in configuration and mounted within the housing 80so that a wall 86A defining the bight portion of the rail 86 facesupwardly to provide a support for the crown portions 40A of the staples40 (FIGS. 3 and 4). At its forward end indicated as 86B (FIG. 3), therail 86 is closed to encircle a rearwardly extending portion 64A of theshear block 64. A compression spring 88 biases the lower wall of theclosed portion 868 of the rail 86 against the adjacent structure 64A toretain the rail 86 in position. This interfitting resiliently biasedconnection of the front end of the rail 86 to the shear block 64 aids incontrolling manufacturing tolerances and prevents wear which mightresult in eccentric or misaligned positioning of the rail 86 relative tothe shear block 64 and the structures defining the drive track 36. Therear end of the rail 86 is secured to the housing 80 in any suitablemanner such as by a member 90 which is secured to the housing 88 bymachine screws 92 (FIG. I and which interfits with the rear end of therail 86.

Strips of staples 40 can be inserted into the magazine 42 to besupported on the rail 86 through the open top of the housing 80. Aplate-like extension 90A on the member 90 (FIGS. 1 and 8) extendsforwardly between the housing side walls and includes two downwardlyinclined legs 90B (FIGS. 1, 8, and 10) straddling the U- shaped rail 86and disposed immediately adjacent depending opposite side walls 86C ofthe rail. The pointed ends at the lower end of the legs 40B of thestaples 40 in a strip can be placed in engagement with the downwardlyinclined legs 908 to guide a strip into the magazine 42 to a position inwhich the legs 40B of the staples in the strip are disposed immediatelyadjacent and extending generally parallel to the rail side walls 86Cwith the crown portions 40A of the staples resting on the upper wall 86Aof the rail 86.

To provide means for resiliently biasing or feeding a strip of staples40 toward the drive track 36 in the nosepiece assembly 38, there isprovided a pusher assembly indicated generally as 96. The pusherassembly 96 is movably mounted on the housing 80 within a pair ofaligned and opposed grooves 99 (FIG. 9) formed in enlarged upper endportions 808 of the side walls of the housing 80. The grooves or slots99 slidably receive the side edges ofa supporting plate 100 to mountthis plate in a position spaced above the wall 86A of the staplesupporting rail 86. A generally U-shaped bracket 102 having a pair ofspaced upstanding side walls 102A is mounted on the upper surface of theplate 100 with the lower end portion of a handle 104 for the pusherassembly 96 disposed between the walls 102A. The handle 104 and thebracket 102 are secured to the plate 100 by a suitable fastener 106. Toprovide means for engaging the staples 40, the pusher assembly 96includes a generally U-shaped pusher member 108 pivoted at one end tothe side walls 102A of the bracket 102 by a pivot pin 110. The oppositeend of the member 108 is provided with two downwardly inclined legs 108Ahaving staple leg engaging portions 108B generally disposed parallel toand in immediate proximity to the side walls 86C of the staple rail 86.To provide means for resiliently biasing the staple legs 108A to theposition shown in FIG. 10, a torsion spring 112 is pro vided having acylindrical center portion which is mounted on the pivot pin 110 betweenthe side walls 102A with the outer free ends bearing against the plate100. An end portion 112A of the torsion spring 112 bears against a bightportion 108C to pivot the pusher element 108 in a counterclockwisedirection about the pivot pin 1 10 to the normal position shown in FIG.10. This position is determined by engagement of the pusher 108 with thetop surface of the plate 100.

To provide means for biasing the pusher assembly 96 toward the nosepieccassembly 38, there is provided a constant force spring 114, one endportion 114A of which is hooked or clamped between the bight of thebracket 102 and the lower wall of the handle 104 to secure the constantforce spring 114 to the pusher assembly 96. The other end of theconstant force spring 114 (FIG. 3) is coiled about a spool 116 (FIGv 3)rotatably mounted within an enclosure indicated generally 118 by a shaftor a pin 120. The constant force spring 114 tends to return to thecoiled position whenever it is extended by moving the pusher assembly 96to the right. This tendency to return to a coiled position pro vides aresilient bias forcing the pusher assembly 96 to the left as shown inthe drawings, and thus forcing the staple leg engaging portions 1088 onthe pusher legs 108A into engagement with the leg 40B of the last staple40 in the strip. The withdrawn portion of the constant force spring 114extending between the spool 116 and the pusher assembly 96 is narrowerthan the upper opening in the magazine housing and is spaced above tooverlie the crowns 40A of the staples 40 in a strip disposed within themagazine assembly 42. The spring 114 passes between the pusher legs108A.

Assuming that a partially consumed strip of staples 40 is disposedwithin the magazine assembly 42 and an additional strip of staples 40 isplaced on the rail 86 disposed to the right of the pusher assembly 96(FIG. 10), the handle 104 is grasped by the operator, and the pusherassembly 46 is moved to the right. As the pusher assembly 96 moves tothe right, the inclined right-hand edges 108B of the two pusher legs108A engage the first staple 40 in the strip to be added, and the pusherelement 108 may either be pivoted in a clockwise direction about thepivot pin 110 to the position shown in dot and dash outline in FIG. 10or engage the first staple 40 in the strip and move the strip rearwardlyuntil the last staple engages legs B whereupon the pusher element 108 ispivoted in the manner described. When the lower ends of the pusher legs108A clear the last staple 40 in the strip to be added, the torsionspring 112 pivots the pusher element 108 in a counterclockwise directionabout the pivot pin 1 10 so that the staple leg engaging portions 10813of the pusher legs 108A and slide down legs 90B and engage the legs 40Bof the last staple 40 in the strip to be added. If the handle 104 isreleased, the extended constant force spring 114 biases the pusherassembly 96 to the left (FIG. 10) to move the first staple 40 in thestrip to be added into en gagement with the last staple 40 in the strippreviously disposed in the magazine assembly 42, and the pusher assembly96 thereafter advances successive staples 40 into the drive track 36 asthey are driven.

To provide means for limiting movement of the pusher assembly 96 to theleft so that the pusher legs 108A cannot enter the drive track 36, adrive or roll pin 122 extends through the side walls 102A and the lowerportion of the handle 104 (FIG. 8) so that the ends of the pin 122extend substantially beyond the side walls 102A. When the pusherassembly 96 reaches the position at which the staple engaging portions108B on the pusher legs 108A are disposed immediately adjacent theentrance to the drive track 36, the projecting ends of the pin 122engage the end surfaces of a pair of plates 124 which are mounted withinrelieved portions along the inner surface of the side walls of thehousing 80 and secured therein by the machine screws 84. The engagementof the ends of the pin 122 with the plates 124 provides a positive stopfor limiting movement of the pusher assembly 96 to the left. as shown inthe drawings.

If the pusher 96 is pulled to an extreme righthand position (FIGS. 8 and10). the inclined right-hand edges of the pusher legs 108A come intocontact with the downwardly inclined legs 90B. This cams the pusherelement 108 in a clockwise direction against the bias of the torsionspring 1 12 to permit the pusher 108 to be manually grasped. The pusherassembly 96 can then be permitted to move to the left with the pusherelement 108 elevated. In this way, by tipping the maga- Zinc 46, stripsof staples 40 can be removed from the rail 86 within the magazinehousing 80.

Drive System The drive system for controlling the reciprocation of thepiston 32 within the slidably mounted cylinder 26 includes the mainvalve assembly 28 which selectively connects the upper interior of thecylinder 26 to the atmosphere or to the compressed air in the reservoir24 as well as controlling the shifting movement of the cylinder 26 toopen and close the exhaust valve assembly 30. The exhaust valve assembly30 opens the lower in' terior of the cylinder 26 prior to and during apower stroke of the piston 32 and seals the lower interior of thecylinder 26 during a return stroke to permit the piston 32 to bepneumatically returned to its normal position.

To provide for slidably mounting the cylinder 26 within the head portion22A, this head portion 22A includes an annular or cylindrical portion22C (FIGS. 3-5) formed integral with the housing 22 within which ismounted a sleeve I30 sealed by the illustrated rings. The cylinder 26 isslidably mounted within the cylindrical sleeve 130, and a similarcylindrical portion 22D formed in the housing 22. To provide means forlimiting the movement of the cylinder 26, the cylinder carries anannular ring 132 sealed by the illustrated 0- rings and bearing againsta shoulder on the cylinder 26. A space 134 between the ring 132 and thesleeve I30 is continuously vented to the atmosphere. Upward movement ofthe cylinder 26 relative to the housing 22 is limited by engagement ofthe ring 132 with the lower surface of the sleeve 130 (FIG. The exposedlower surface of the ring 132 provides a continuous upwardly directedpneumatic bias tending to shift the cylinder 26 to the elevated positionshown in FIG. 5. The selective movement of the cylinder between theupper position shown in FIG. 5 and the lower position shown in FIG. 3 iscontrolled by the main valve assembly 28.

More specifically. the main valve assembly 28 includes an annular mainvalve member 136, an upper annular piston portion 136A of which isslidably mounted within an annular chamber 138 formed in a closure cap140 and surrounding a central hollow post 140A on the closure cap 140. Aplurality of depending lugs 1408 on the cap bear against the upper endof the sleeve 130 to mechanically hold the sleeve I30 in position. Acircular exhaust valve member 142 secured to the cap by a fastener 144is disposed within a central opening in the annular valve 136. Aplurality of compression springs 148 interposed between the cap 140 andthe upper surface of the main valve element 136 together with thepressurized fluid normally supplied to the chamber I38 above the pistonportion 136A normally hold the main valve element 136 in the positionshown in FIG. 3 in which a resilient valve element I50 engages the upperend of the cylinder 26 to hold this cylinder in the position shown inFIG. 3. The resilient valve element 150 closes off communication betweenthe upper interior of the cylinder 26 and the compressed air containedin the surrounding reservoir 24. In this position, the interior surfacesof the annular valve I36 are spaced from the exhaust valve member I42 sothat the upper interior of the cylinder 26 is connected to theatmosphere through a plurality of passageways 152 in the closure capI40.

To provide means for controlling the shifting movement of the annularmain valve element 136, there is provided a dump valve assemblyindicated generally as 154. The dump valve assembly 154 includes aplural diameter valve element 156 carrying the illustrated sealingO-rings and slidably disposed within a cylinder 158 formed in the cap140. A compression spring 160 continuously biases the valve element tothe left-hand position shown in FIG. 3. The bias provided by the spring160 is supplemented by pressurized fluid supplied to the right-hand endof the cylinder 158 over a passageway 162 in the closure cap which isplaced in communication with the control valve assembly 44 by a conduitI64 (FIGS. 3S). In the normal condition of the tool, pressurized fluidis supplied to the conduit or duct 164 by the control valve assembly 44.This pressurized fluid in the right-hand end of the cylinder 158 coupledwith the resilient bias of the spring forces the valve piston 156 to theposition shown in FIG. 3. In this position, the pressurized fluid fromthe reservoir 24 passes from a passageway I66 in the closure cap intothe chamber 138 through a passageway 168.

When the main valve assembly 28 is to be operated, the conduit 164 isconnected to the atmosphere by the control valve assembly 44, and thepressurized fluid supplied through the passageway I66 acts on theenlarged right-hand portion of the valve piston I56 to shift this valvepiston against the bias of the compression spring 160 to the positionshown in FIG. 5. In this position, the passageway 168 is cut off fromcommunication with the passage I66, and pressurized fluid from thereservoir 24 can no longer be supplied to the chamber 138. Further, thepassageway I68 and an additional passageway 170 are connected to theatmosphere through the passageways 152 by means of a port 172 that isnow opened by the displacement of the valve piston 156.

When the dump valve assembly moves to the position shown in FIG. 5,pressurized fluid in the chamber 138 above the piston portion 136A onthe annular main valve I36 is exhausted to the atmosphere through thepassageways 168 and 170, the port 172, and the passageways I52. Thepressurized fluid in the reservoir acts on the lower effective surfacesof the main valve 136 to move this valve upwardly toward the positionshown in FIG. 5 against the resilient bias of the compression Springs148. During the first portion of this movement. the cylinder 26, becauseof the continuous upwardly directed bias applied to the ring 132, moveswith the main valve 136, and the resilient element 150 remains seated onthe upper end of the cylinder 26. When the upper surface of the ring I32bears against the lower surface of the sleeve 130, the cylinder 26 canno longer move upwardly. During further movement of the main valveelement I36, an O-ring I74 carried on the inner surface of the annularmain valve element I36 seats on the outer periphery of the exhaust valvemember 142 to close off communication between the upper interior of thecylinder 26 and the exhaust passageways 152 in the cap. Further upwardmovement of the main valve I36 moves the resilient element I50completely out of engagement with the now stationary cylinder 26 so asto connect the upper interior of the cylinder 26 to the reservoir 24 ofpressurized fluid. This initiates a power stroke of the piston 32 andthe connected driver blade 34.

When the main valve assembly 28 is to be closed, the control valveassembly 44 again supplies pressurized fluid over the conduit I64 andthe passageway 162 to the right-hand end of the cylinder 158. Thispneumatic bias coupled with the bias of the compression spring 160shifts the valve piston 156 from the position shown in FIG. to theposition shown in FIG. 3. In this position. the port 172 is closed, andthe passageways 166 and 168 are placed in communication so thatpressurized fluid again flows into the chamber 138 above the pistonportion 136A of the main valve element 136. This pneumatic bias coupledwith the resilient bias pro-- vided by the compression springs 148initiates downward movement of the main valve element 136 from theposition shown in FIG. 5 to the position shown in FIG. 3. During theinitial movement, the resilient O- ring 150 seats on the upper end ofthe cylinder 26 so that the upper interior of the cylinder 26 is cut offfrom communication with the pressurized fluid in the reser voir 24.During subsequent movement, the O-ring 174 is moved downwardly enough toplace the cylinder 26 in communication with the exhaust passageways 152to exhaust the upper end of the cylinder. Continuing downward movementof the annular main valve 136 moves the cylinder 26 downwardly from theposition shown in FIG. 5 to the position shown in FIG. 3. In thisposition, the piston 32 and the driver blade 34 can be moved through areturn stroke to restore the drive system to its normal condition.

Associated with the sliding cylinder 26 and the main valve assembly 28is an assembly for providing the control valve assembly 44 with signalsrepresenting the position of the piston 32. More specifically, thecylindrical portion 22C of the housing is provided with a hollowprojection 176 (FIGS. 35) communicating with the control valve assembly44 over a duct or conduit 178. A plug 180 (FIG. 4) with a restrictedorifice therethrough places a chamber 182 in communication with thepressurized fluid in the reservoir 24. The chamber I82 is placed incommunication with the exterior of the sleeve 130 (FIGS. 3 and 5)through an opening or port 184 (FIG. 4). The outer surface of the sleeve130 (FIGS. 3 and 5) is, in turn. placed in communication with a port orpassageway 186 through the upper end of the cylinder 26 by means of apassageway 187 through the sleeve 130. These passageways are sealed bythe illustrated O-rings.

When the piston 32 occupies the normal position shown in FIG. 3, the twoillustrated O-rings on the piston 32 seal the passageways 186 and 187 sothat the chamber 182 (FIG. 4) and thus the conduit 178 extending to thecontrol valve assembly 44 becomes pressurized to the pressure of thecompressed air in the res ervoir 24. This signal indicates that thepiston 32 is in its normal home position. Alternatively. when the piston32 is displaced from its normal position through a power stroke and themain valve assembly 28 has again been closed at the termination of thispower stroke, the upper interior of the cylinder 26 is placed at atmospheric pressure in the manner described above. At this time. thepassageways I86 and I87 and the port 184 vent the chamber 182 and theduct 178 to the atmosphere because these passageways exhaust pressurizedair faster than it can be supplied through the restricted orifice in theplug 180. Thus. when the main valve assembly 28 is closed and the piston32 is not in a normal home position, the conduit 178 provides an exhaustsignal to the control valve assembly 44. When the piston 32 is returnedto its normal position. the port 186 is again sealed, and the restrictedorifice in the plug I80 (FIG. 4) again pressurizes the chamber 182 andthe conduit 178 to advise the control valve assembly 44 that the piston32 has been returned to its normal home position.

To provide the exhaust valve assembly is for selectively sealing oropening to the atmosphere the lower interior of the cylinder 26, thereis provided an annular or cylindrical member 188 (FIGS. 3, 5, and 6)whose lower end is welded or otherwise permanently secured to anuppermost plate 48A in the four laminated plates 48A-48D in the plateassembly 48. The annular memher 188 includes an enlarged upper endportion 188A having a recess in which is disposed a resilient O-ring 190providing an exhaust valve seal. The element 190 is aligned with thelower end of the cylinder 26.

In the normal condition of the tool 20 (FIG. 3), the engagement of theupper end of the cylinder 26 by the main valve 136 or the resilientelement thereon seats the lower end of the cylinder 26 on the resilientelement to close off communication between the lower interior of thecylinder 26 and the atmosphere through, for example, a plurality ofspaced ports or openings 192 (FIGS. 3, 5, and 6). When, however, themain valve assembly 28 is opened (FIG. 5), the cylinder 26 is movedupwardly in the manner described above, and the lower end of thecylinder 26 is spaced from the resilient element 190. This places thelower interior of the cylinder 26 beneath the piston 32 in communicationwith the atmosphere through the openings 192. The entire lower end ofthe cylinder 26 is vented through the large area openings I92, and thusno back pressure is encountered by the piston 32 during its drivingstroke. This substantially improves the efficiency of the drive systemfor the tool 20.

Associated with the exhaust valve assembly 30 is a unique fluidconveying means controlled by the control valve assembly for supplyingpressurized fluid to the lower interior of the cylinder 26 to move thepiston 32 through a return stroke. More specifically, this pressurizedfluid is supplied by the control valve assembly 44 to a passageway 194(FIGS. 4, 6, and 8), which passageway extends through a dependingportion of the head portion 22A of the housing 22 immediately adjacentone of the tapped openings 54 used to secure the plate assembly 48 tothe head portion 22A. This pas sageway 194 is aligned with an opening196 in the uppermost plate 48A, and the port or passageway 196 is, inturn. aligned with a pair of elongated passageways 198 in the plates 48Band 48C at the right-hand end thereof. The elongated slots 198 extendthrough the plates 48B and 48C to a point underlying an opening 200(FIGS. 6 and 8) in the uppermost plate 48A. The opening 200 extendsthrough the plate 48A to discharge air within the annular member 188.

A resilient or elastomeric bumper or cushion 202 is disposed within andheld in position by the annular member 188 in a position to cushion orterminate the power stroke of the piston 32. The bumper 202 includes aplurality of radially extending, tapered ribs 202A terminating above theplate 48A so that pressurized fluid supplied through the opening 200 canbe dispersed around the periphery of the bumper 202 through a passage203 and then pass downwardly through the passageways defined by the ribs202A to be applied to the lower surface of the piston 32 when thispiston is in its lower position (FIG. 7). The pressurized return airsupplied through the opening 200, in passing through the passagewaysdefined by the ribs 202A, cools the bumper 202 to prevent deteriorationan! overheating thereof. By thus supplying piston return air over thesystem of passageways 194 and 196 and 198 and 200, and then dispersingthis air around the exte rior surface of the bumper 202, the pistonreturn air not only is supplied directly beneath the piston 32 withoutpassing through the side walls of the cylinder 26, but is also used toeffect cooling of the bumper 202. Further, the use of the laminatedplate assembly 48 facilitates the formation of the passageways in aconstruction of welded or brazed individual plates which are capable ofabsorbing the impact shocks arising from terminating the power stroke ofthe piston 32.

Associated with the exhaust valve assembly 30 is an improved arrangementfor supplying a signal to the control valve assembly 44 indicating thatthe piston 32 has completed its power stroke. This arrangement is bestillustrated in FIG. 7 of the drawings. More specifi cally, when thepiston 32 reaches the end of its power stroke, as determined byengagement with the bumper 202, pressurized fluid from above the piston32 flows out of the cylinder through a plurality of spaced ports 204 toan area in the interface between the cylinder 26 and the portion 22D ofthe head 22A of the housing. A passageway through the portion 22D of thehead 22A supplies this pressurized signal to the control valve assembly44. In the past, there has been a tendency for this end of power strokesignal of pressurized fluid to become dissipated when the interior ofthe cylinder 26 above the piston 32 is exhausted by closing the mainvalve to start the return stroke of the piston 32.

However, in the present arrangement, as soon as the signal suppliedthrough the ports 204 controls the control valve assembly 44 to effectthe closing of the main valve, the cylinder 26 is moved downwardly fromthe position shown in FIG. 7 to the position shown in FIG. 3 in whichthe lower end of the cylinder 26 seats on the exhaust valve seat 190.When this happens, the ports 204 are moved to a position bounded onopposite sides by the two O-rings carried on the piston 32. Thepressurized signal supplied through the ports 204 is thus sealed offfrom communication with either the upper or lower interior of thecylinder 26. Further, when compressed air is supplied through theopening 200 be neath the piston 32 to start the return stroke of thepiston 32, this pressurized fluid also passes through the ports 204 tosupplement the cycle valve bias previously supplied from the pressurizedfluid above the piston 32 which may now have been exhausted to theatmosphere by the closure of the main valve assembly 28.

Control Valve Assembly 44 The control valve assembly 44 is controlled bya manually actuated trigger 206 and a conventional workpiece engagingassembly indicated generally as 208 to operate the fastener driving toolthrough one or a number of automatically effected cycles of power andreturn strokes of the piston 32. The mechanical construction ofthecontrol valve assembly 44 can be of any suitable type and can, forexample, be of the gen eral nature disclosed and described in US. Pat.No. 3,685,396. In general, the control valve assembly is carried in ahousing 210 as an integral subassembly which can be secured to a wall ofthe head portion 22A of the housing 22 by suitable fasteners, such asmachine bolts or screws 212 (FIG. 4). The passages in the valve housing210 communicating with the various control components of the assembly 44are coupled to ports terminating related passageways formed in thehousing 22. The valve housing 210 is provided with a pair of spacedsupporting lugs 210A between which the trigger 206 is pivotally mountedon a pivot pin 214 (FIGS. 1 and 4).

The workpiece engaging assembly or means 208 which is actuated when thetool 20 is placed adjacent a workpiece can be of any suitable well knownconstruction, such as that shown in US. Pat. No. 3,615,049. In general,the assembly 208 includes a linkage 216 mounted on the housing 22 andthe nosepiece assembly 38 and resiliently biased to a position in whicha workpiece engaging portion 216A of the mechanism projects downwardlybelow the lower end of the nosepiece assembly 38. An upper portion 2168is coupled by a lost motion arrangement to the lower end of a safetyvalve stem 218 (FIG. 3) forming a part of the control valve assembly 44.When the tool 20 is placed adjacent a workpiece, the lower end portion216A engages the workpiece and moves the mechanism 216 upwardly. Afterthe lost motion has been taken up, the portion 2168 of the linkage 216moves the safety valve stem 218 upwardly from a normal position shown inFIG. 11 to an actuated position shown in FIG. 12. When the tool 20 ismoved away from the workpiece, resilient biasing means 220 (FIG. 1 movesthe linkage 216 downwardly so that after the lost motion is taken up, aportion 216B moves the valve stem 218 downwardly from the actuatedposition shown in FIG. 12 to the normal position shown in FIG. 11.

Referring now more specifically to the valving arrangement included inthe control valve assembly 44, the assembly 44 is shown in normalposition in FIG. 11 and in an operated position in FIG. 12. The controlvalve assembly includes a return air valve assembly in dicated generallyas 222, a combined manual-safety valve assembly indicated generally as224, and a cycle valve assembly indicated generally 226. To provide amaster source of pressurized fluid or compressed air for use by thecontrol valve assembly 44, there is provided a port or passageway 228extending from the reservoir 24 through a wall of the housing 22 and theback wall of the housing 210 to the control valve assembly 44 to openinto a valve cylinder 230 forming a part of the return valve assembly222. A passageway 232 forwards this pressurized fluid to a valvecylinder 234 forming a part of the manual valve assembly 224. A furtherpassageway 236 forwards this pressurized air to a valve cylinder 238forming a part of the cycle valve assembly 226.

The manual-trigger valve assembly 224 is actuated by the trigger 206 andthe workpiece engaging assembly 208 to selectively connect a passageway240 coupled to the cycle valve assembly 226 to a source of pressurizedfluid when the control valve assembly 44 is in its normal position andto connect the passageway 240 to the atmosphere when the assembly 224has been properly actuated by the trigger 206 and the workpiece engagingassembly 208. The manual valve assembly 224 includes the safety valvestem 218 having therein a valve chamber 242 open at its upper end to theatmo sphere. Slidably disposed within the valve chamber or cylinder 242is a valve element or stem 244 with an en larged upper end portion 244A.A compression spring 245 interposed between the lower end of the valvestem 244 and the lower wall of the valve chamber 242 normally biases thevalve stem 244 to the position shown in FIG. 11. The pressurized fluidadmitted to the interior of the chamber 242 through a plurality ofpassageways 246 from the valve cylinder 234 and the passageway 232 alsoacts on the enlarged portion 244A to aid the bias of the spring 245 andnormally seat this enlarged portion 244A on an exhaust valve O-ring 248.The spring bias insures that the tool will not fire when first coupledto pressurized air. This pressurized fluid also passes outwardly fromthe chamber 242 through a plurality of ports or passageways 250 and theportion of the valve chamber 234 bounded by the illustrated O-rings tobe conveyed over the passageway 240 to the cycle valve assembly 226.

When the valve stem 218 is moved upwardly to its actuated positiondetermined by engagement of the upper stem 218 with a shoulder formed inthe valve cylinder 234 (FIG. 12) and when the trigger 206 is pivoted ina counterclockwise direction about the pivot pin 214 to the positionshown in FIG. 5, the indicated portion of the trigger 206 movesdownwardly into engagement with the upper end of the valve stem 244 andshifts this valve stem to the position shown in FIG. 12. In thisposition, an O-ring 252 seats on the inner wall of the valve chamber 242to close off communication between the ports or passageways 246 and 250to terminate the supply of pressurized fluid to the passageway 240. Atthe same time. the enlarged upper end portion 244A of the valve element244 moves out of engagement with the O-ring 248 to connect thepassageway 240 to the atmosphere. The valve means 244 cannot be moved tothe position shown in FIG. [2 unless both the safety valve stem 218 iselevated to the position shown and the trigger 206 is depressed to theposition shown. Thus, the manual-safety valve assembly 224 cannot beoperated to connect the passageway 240 to the atmosphere unless both thetrigger 206 and the workpiece engaging assembly 208 are actuated. Therelease of these elements restores the manual valve assembly 224 to itsnormal position shown in FIG. ll so that pressurized fluid is reappliedto the passageway 240 and its communication with the atmosphere isinterrupted.

The return air valve assembly 222 is controlled by the pressure in theupper interior of the drive cylinder 26 to selectively supply return airto the lower end of the cylinder 26 at the end of a power stroke and toterminate this supply of return air when the piston 32 is re stored toits normal position. In addition. the return air valve assembly 222supplies a supplemental source of pressurized air for preventingpremature operation of the cycle valve assembly 226. The return airvalve assembly 222 includes a valve piston 254 slidably mounted in thevalve chamber 230 and having an upper greater area piston portion 254Aand a lower smaller area piston portion 2548 providing a bias oppositelydirected to that provided by the piston portion 254A. The pressurizedfluid normally supplied through the conveying means 178 in the mannerdescribed above acts on the piston portion 254A to provide a greatermagnitude downwardly directed bias acting on the valve piston 254 thanis provided by the pressurized fluid supplied by the passageway 228 tothe valve chamber 230 which provides an upwardly directed bias acting onthe piston portion 254B. Thus, the valve piston 254 normally occupiesthe position shown in FIG.

11 in which its lower end seats on a resilient O-ring 256.

When the drive piston 32 reaches the end of its power stroke and themain valve assembly 28 is closed to exhaust the upper interior of thecylinder 26, the conduit 178 is placed at atmospheric pressure, and thebias is removed from the large piston portion 254A on the valve piston254. At this time the pressurized fluid supplied to the lower end of thevalve cylinder 230 by the passageway 228 acts on the small area pistonportion 254B to move the valve piston 254 upwardly to the position shownin FIG. 12. At this time, the lower end of the valve piston 254 movesout of engagement with the valve seat 256, and pressurized fluid fromthe passageway 228 and the valve cylinder 230 enters a passageway 258 tobe forwarded through a port 260 to the passageway 194 (FIGS. 4 and 8) tobe supplied in turn through the opening 200 to the lower end of thecylinder 26. In addition, pressurized fluid from the passageway 258 isforwarded over another passageway 262 to be supplied to the lower end ofthe valve chamber 238 for the cycle valve assembly 226. The pressurizedfluid supplied by the passageway 262 is used to avoid a pre maturechange in the state of the cycle valve 226.

When the drive piston 32 has been restored to its normal position in themanner described above. the conduit 178 is again pressurized, and thegreater bias applied by the large piston portion 254A returns the valvepiston 254 to the normal position shown in FlG. 11 so that the supply ofpressurized fluid to the passageway 258 is terminated. The pressurizedfluid trapped in the passageways 258, 260, and 262 is discharged to theatmosphere over the connection through the opening 200 to the lower endof the interior of the cylinder 26. From the closed cylinder, trappedfluid can leak to the atmosphere through clearances along the driverblade 34.

The cycle valve assembly 226 illustrated in FIGS. 1] and I2 is one thatautomatically and successively cycles the main valve assembly 28 betweenopen and closed conditions after the manual valve assembly 224 has beenoperated to produce a sequence of power and re turn strokes of thepiston 32 and the driver blade 34. To accomplish this, the control valveassembly 226 in cludes a valve piston 264 movable to a position causingopening of the main valve 28 by a continuous bias and movable to analternate position closing the main valve assembly 28 in accordance withthe high pressure signal received through the ports 204 (FIG. 7) and 280(FIG. II) when the piston 32 has reached the end of its power stroke. Acontrol piston 266 slidabl y mounted within the valve cylinder 238 forthe cycle valve assembly 226 also forms a part of this assembly and iscon trolled by the return air valve assembly 222 to prevent prematurereturn of the valve piston 264 to its setting effecting opening of themain valve 28.

More specifically, the cycle valve piston 264 which is slidably mountedwithin the valve cylinder 238 includes a small area piston portion 264Aslidably mounted within a reduced diameter cylinder 268 formed in aplug'270 that is carried within an opening 272 in the housing 22Bimmediately above and in alignment with the valve chamber 238 in thevalve housing 210. The chamber 268 is continuously supplied withpressurized fluid from the reservoir 24 through a restricted orifice 274formed in the plug 270. This pressurized fluid acts on the smalldiameter portion 264A to continuously bias the cycle valve piston 264 tothe normal position shown in FIG. 11.

In this position, pressurized fluid normally supplied by the manualvalve assembly 224 over the passageway 240 passes around an O-ring 276in an enlarged portion 238A of the valve chamber to be forwarded over apassageway 278 to one end of the conduit 164. As described above, theconduit 164 extends to the dump valve assembly 154 (FIG. 3) in theclosure cap 140 for the tool and holds the main valve assembly 28 in aposition closing the open upper end of the cylinder 26. When themanual-safety valve assembly 224 is operated in the manner describedabove to connect the passageway 240 to the atmosphere, the conduit I64and the passageway 278 are also connected to the atmosphere to effectopening of the main valve assembly 28 in the manner described above. Inthis operation, the lower exhaust valve assembly opens first, theexhaust passageways I52 are then closed, and finally compressed air isadmitted to the top of the cylinder 26.

When the piston 32 reaches the end of its power stroke (FIG. 7),pressurized fluid is supplied through the ports 204. This pressurizedfluid is conveyed through a passageway 280 extending through the portion22D of the head portion 22A and the back wall of the housing 210 for thevalve assembly 44 to supply this fluid below a large area piston portion26413 on the cycle valve piston 264. This fluid is supplied above theupper surface of the control piston 266. The pressurized fluid suppliedthrough the passageway 280 pro vides a greater upwardly directed biasthan the pressurized fluid acting on the small area piston portion 264A.Thus, the cycle valve piston 264 is moved upwardly from the positionshown in FIG. 11 to the position shown in FIG. 12. When the piston 264moves to the position shown in FIG. 12, the O-ring 276 closes offcommunication between the passageways 240 and 278 so that the conduitI64 is no longer connected to the atmosphere. In addition, an O-ring 282moves into the enlarged portion 232A of the valve cylinder 238 andplaces the passageway 278 in communication with the pressurized fluidsupplied to the valve chamber 238 by the passageway 236. When theconduit 164 is again pressurized, the main valve assembly 28 is closedto terminate the supply of pressurized fluid above the piston 32 andthen to connect the upper interior of the cylinder 26 to the atmosphere.Further, when the main valve assembly 28 is closed, the cylinder 26 isthen moved downwardly to close the lower end exhaust valve assembly 30(FIG. 3). In this position, the O-rings on the piston 32 seal the ports204 so that the pressurized fluid applied to the piston portion 264Bcannot be dissipated. This aids in holding the cycle valve piston 264 inthe elevated position shown in FIG. 12.

When the pressure within the upper interior of the cylinder 26 becomessufficiently dissipated, the return air valve assembly 222 is opened, asshown in FIG. 12, and pressurized fluid is applied over the passageways258 and 262 to the extreme lower end of the cycle valve cylinder 238.This pressurized fluid, in being sup plied directly from the reservoir24 without appreciable throttling, is of greater pressure than thattrapped above this control piston and supplied through the signalpassageway 280. Accordingly. the control piston 266 moves upwardly tothe position shown in FIG. I2. The piston 266 may not physically engagethe large pis ton portion 2648 of the cycle valve piston 264 undercertain conditions where the pressure supplied by the port 280 is greatenough. In any event, the control piston 266 provides an additional biasurging the piston 264 upwardly to the position shown in FIG. 12 againstthe bias applied to the small area piston portion 264A with the resultthat the cycle valve piston 264 cannot be prematurely restored to itsalternate setting shown in FIG. 11.

The opening of the return air valve assembly 222 also suppliespressurized fluid in the manner described above to the lower interior ofthe cylinder 26 so that the piston 32 is elevated toward its normalposition. As the piston 32 clears the ports 204 (FIG. 7), the signal airsupplied to the large piston portion 264B begins to dissipate over thepassageway 280 due to expansion of air within the lower interior of thecylinder 26. However, the pressure of this air is supplemented by thatsupplied by the return valve assembly 222 so that a substantial biasremains applied to the large piston portion 2648. In addition, thecontrol piston 266 provides a continuing bias acting on the large pistonportion 2648 to prevent any movement of the cycle valve piston 264 atthis time.

When the piston 32 is returned to its normal home position, the conduit178 is pressurized, and the return valve assembly 222 is moved to theclosed position shown in FIG. 1 1. This terminates the supply of returnair beneath the piston 32 and beneath the control piston 266. The airacting on the piston 266 becomes dissipated primarily by leakage aroundthe driver blade 34, and the bias resulting from the pressurized fluidwithin the chamber 268 acting on the small piston portion 264A is noweffective to move the cycle valve piston 264 to the normal positionshown in FIG. 11 along with the control piston 266. When the cycle valvepiston 264 reaches the position shown in FIG. 11, the O- ring 282 closesoi? communication between the passageway 278 and the fluid pressuresupplying passageway 236. The O-ring 276 in moving into the enlargedportion 238A connects the passageway 278 to the exhaust passageway 240so that the main valve 28 is again opened. This initiates another cycleof operation of the drive system for the tool 20. This operationcontinues, providing successive cycles of alternate power and returnstrokes until such time as the manualsafety valve assembly 224 isreleased.

The cycle valve assembly 226 can also easily be modified to providesingle cycle rather than autoflre operation. The only change that isrequired is to replace the plug 270 with another plug of identicalconfiguration except that the passageway 274 instead of extendingaxially within the opening 272 to place the chamber 268 in communicationwith the reservoir 24 extends laterally through the plug 270 tocommunicate with a passageway 290 leading to the atmosphere. This, ineffect, removes the autofire bias applied to the small area pistonportion 264A. With this modification, a small area piston portion 264Cis effective when the passageway 240 is pressurized to hold the piston264 for the cycle valve assembly 226 in the normal position shown inFIG. 11. However, when the valve piston 264 is shifted to its elevatedposition shown in FIG. 12 in precisely the manner described above, thepiston portion 264C is connected to the atmosphere over the passageway240, and no bias exists for returning the piston 264 to the normalposition shown in FIG. 1] until such time as the manual-safety triggerassembly 224 is released to repressurize the passageway 240. With thismodification, the cycle valve assembly 226 operates the tool 20 througha single power and return stroke, and further power strokes cannot beinitiated until the manualsafety valve assembly 224 is released.

Referring now more specifically to FIG. 13 of the drawings, therein isillustrated a schematic diagram of the control valve assembly 44 foreffecting autofire operation of the tool 20. The main valve assembly 28,in its schematic form shown in FlG.. 13, includes the dump valveassembly 154. A small effective area piston portion 28A shown in FIG. 13represents the lower area of the main valve element 136 tending to openthis valve. A large effective area piston portion shown as 288 in FIG.13 represents the upper effective area of the piston portion 136A aswell as the bias applied by the compression springs 148. Since the biasprovided by the large area piston portion 28B overcomes the biasprovided by the piston portion 28A, the main valve 28 in its normalposition connects the upper interior of the cylinder 26 to theatmosphere. The large area piston portion 283 is normally connected topressurized fluid over the passageways 164, 240, the cycle valve 226,and the manual-safety valve assembly 224.

When the tool 20 is to be operated, and both the trigger 206 and theworkpiece engaging assembly 208 are operated, the manual-safety valveassembly 224 is operated to its alternate setting, and the lines 164 and240 connect the large piston portion 288 on the main valve assembly 28to the atmosphere. The continuous bias applied to the small area pistonportion 28A shifts the main valve assembly 28 to its open position sothat the lower exhaust valve assembly 30 is first opened, the exhaustpassages 152 are next closed, and finally pressurized fluid is appliedto the upper interior of the cylinder 26. This moves the piston 32 andthe driver blade 34 through a power stroke to drive a staple 40 suppliedto the drive track 36. At the end of the power stroke of the piston 32,pressurized fluid collected through the ports 204 is supplied over thepassageway 280 to pressurize the large piston portion 26413 of the cyclevalve assembly 226.

The force applied by the large area piston portion 264B overcomes thecontinuous bias applied to the small area piston portion 264A, and thecycle valve 226 shifts to its alternate setting so that even though theline 240 remains at atmospheric pressure, the passageway 164 is againpressurized, and the large area piston portion 288 shifts the main valveassembly to its normal setting shown in FIG. 13. Incident to this, theexhaust valve assembly 30 for the lower interior of the cylinder 26 isclosed.

When the upper interior of the cylinder 26 approaches atmosphericpressure, the port 186 exhausts the passageway or conduit 178 fasterthan pressurized fluid can be supplied through the restricted orifice inthe plug [80, and the large area piston portion 254A of the return airvalve assembly 222 becomes substantially depressurized. At this time,the continuous pneumatic bias applied to the small area piston portion2548 is effective to operate the return air valve assembly 222 to itsalternate setting. When this happens, the line 258 is pressurized tosupply fluid pressure over the passageway 262 to the control piston 266.The control piston mechanically biases the cycle valve assembly 226toward its alternate setting to supplement the pneumatic bias applied bythe large piston portion 2643.

The pressurized fluid supplied to the passageway 258 is also supplied tothe opening 200 below the piston 32 in the cylinder 26 over a system ofpassageways and ports including the components 194, 196, 198, and 200.This pressurized fluid moves the piston 32 upwardly through a returnstroke toward its normal position. As the piston 32 clears the ports204, pressurized fluid from the opening 200 also passes out of thecylinder 26 through the ports 204 to be applied over the passageway 280to supplement the bias applied to the large area piston portion 2648 onthe cycle valve 226. When the piston 32 reaches its normal homeposition, the ports 186 are sealed from communication with theatmosphere by the O-rings carried on the piston.

The orifice in the plug then begins to pressurize the passageway 178.When this becomes sufficiently pressurized, the bias applied to thelarge piston portion 254A on the air return valve 222 shifts this valveto the normal position shown in FIG. 13 against the continuous biasapplied to the small area piston portion 254B. When this happens, thepassageway 258 and the passageways connected thereto tend towardatmospheric pressure along with the passageway 280, by, for example,leakage of air from the bottom of the cylinder 26 along the sides of thedriver blade 34. When this pressure drop becomes great enough, thecontinuous bias applied to the small area piston portion 264A of thecycle valve assembly 226 shifts this cycle valve back to its normalposition shown in FIG. 13 and restores the control piston 266 to itsnormal position.

With the cycle valve 226 in its normal position, the passageway orconduit 164 is again connected to atmosphere over the passageway 240 andthe operated valve assembly 224. This opens the main valve assembly 28in the manner described above. This cyclic operation continues untilsuch time as the manual-safety valve assembly 224 is released. At thistime, the control components of the control valve assembly 44 arerestored to the normal position shown in FIG. 13.

Although the present invention has been described with reference to anumber of illustrative embodiments thereof, it should be understood thatnumerous other modifications and embodiments can be devised by thoseskilled in the art that will fall within the spirit and scope of theprinciples of this invention.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

l. A tool for driving fasteners into a workpiece comprising a poweredfastener driving assembly including a driver element actuated by a drivepiston slidable within a drive cylinder,

:1 fluid controlled main valve means opened to supply pressurized fluidto and closed to exhaust fluid from the cylinder to move the pistonthrough power and return strokes,

a cycle valve coupled to the main valve means and operable to alternatepositions to open and close the main valve means, said cycle valve beingbiased to a position to close the main valve means, said cycle valvealso including valve piston means,

passage means coupling the valve piston means to the drive cylinder toreceive pressurized fluid for biasing the cycle valve to a position toclose the main valve means,

return valve means responsive to the exhaust of the drive cylinder abovethe drive piston for supplying pressurized fluid into the drive cylinderbelow the drive piston to move the drive piston through a re turnstroke, the pressurized fluid below the drive piston being supplied tothe valve piston means to bias the cycle valve to a position to closethe main valve means,

and means responsive to the completion of the return stroke of the drivepiston for controlling the return valve means to terminate the supply ofpressurized fluid to the drive cylinder below the piston means and thusto the valve piston means.

2. A tool as set forth in claim 1 including a bias piston movable intoengagement with the valve piston means,

and means coupling the bias piston to the return valve means to receivepressurized fluid from the return valve means,

3. A tool as set forth in claim 1 including a valve seat adjacent thelower end of the drive cylinder communicating with the atmosphere,

and means movably mounting the drive cylinder for movement intoengagement with the valve seat when the main valve means is closed andout of engagement with the valve seat when the main valve means isopened to exhaust the drive cylinder below the piston.

4. A tool as set forth in claim 3 including port means in the cylinderforming a part of said passage means, said port means being opened topressurized fluid in the drive cylinder above the drive piston when thecylinder is out of said engagement with the valve seat and the drivepiston is at the end of its power stroke, said port means being closedby said drive piston when the drive cylinder engages said valve seat andthe drive piston is at the end of its power stroke.

5. A tool for driving fasteners into a workpiece comprising a housing,

a cylinder slidably mounted in the housing and slidably receiving apiston movable through power and return strokes,

fastenerdriving blade actuated by the piston,

a main valve means opened to supply a pressurized fluid to the top ofthe cylinder and closed to exhaust fluid from the top of the cylinder,said main valve means including means engaging the cylinder to move thecylinder down when the main valve means is closed and permitting upwardmovement of the cylinder when the main valve means is opened,

a nosepiece structure on the housing adjacent the lower end of thecylinder and having a drive track through which the fastener drivingblade extends,

a cylindrical valve seat engaged by the lower end of the cylinder whenthe main valve means is closed and spaced below the lower end of thecylinder when the cylinder moves upwardly as the main valve means isopened, the space between the valve seat and the lower end of thecylinder exhausting the lower interior of the cylinder,

a fluid actuated cycle valve means coupled to the main valve means andautomatically operable through a sequence of two spaced positions toopen and close the main valve means, said cycle valve means includingmeans responsive to pressurized fluid from the lower end of the cylinderto effect closure of the main valve means,

a fluid controlled return valve means responsive to the closure of themain valve means for supplying pressurized fluid to the cycle valvemeans to hold the main valve means closed and to the lower end of thecylinder below the piston to move the piston through a return stroke,said fluid controlled return valve means being released to terminate thesupply of pressurized fluid when the piston completes its return stroke,

and control means for initiating movement of the cycle valve means tostart a power stroke of the piston.

6. A tool as set forth in claim 5 in which the cylindrical valve seat isfixedly secured to and projects upwardly from the nosepiece structure,

and the return valve means is carried on the housing and includespassage means through the housing and nosepiece structure terminating ina discharge port disposed within the cylindrical valve seat.

7. A tool for driving fasteners into a workpiece comprising a housingdefining a chamber,

a cylinder slidably mounted within the chamber for limited movement,

a fluid actuated main valve assembly movable into and out of engagementwith the top portion of the cylinder, said cylinder being fluid biasedtoward the main valve assembly and movable over a limited travel withthe main valve assembly before separation of the top portion of thecylinder and the main valve assembly,

a piston slidable within the cylinder,

a fastener driving blade actuated by the piston,

a nosepiece structure on the housing adjacent the lower end of thecylinder and defining a drive track slidably receiving the fastenerdriving blade,

an annular member fixedly secured to the nosepiece structure encirclingthe fastener driving blade and aligned with the lower portion of thecylinder,

a resilient sealing element carried on the annular member adapted to beengaged by the lower portion of the cylinder when the main valve meansis moved into engagement with the top of the cylinder to move thecylinder down into seating engagement with the sealing element, saidsealing element being spaced from the lower portion of the cylinder whenthe main valve assembly is moved upwardly out of engagement with thecylinder to permit limited upward movement of the cylinder away from thesealing element,

a fluid passage passing through the housing and the nosepiece structureand having a port in the nose piece structure within the annular member,

and fluid control means coupled to the main valve assembly and to thefluid passage to move the main valve assembly into and out of engagementwith the top portion of the cylinder and to supply fluid to the fluidpassage.

8. A tool for driving fasteners comprising a tool housing with anosepiece structure including a drive track,

power actuated fastener driving means on the tool housing including adriver element movable in said drive track,

a magazine housing with an open top coupled to the nosepiece structureand having a fastener supporting structure disposed below said open topfor supporting and feeding a series of fasteners-into the drive track,

a pusher carriage mounted on said housing for movement toward and awayfrom the drive track along an elongated path,

a rigid fastener engaging pusher element for engaging fasteners on saidfastener supporting structure,

pivot structure coupling the pusher carriage and the pusher element tomount the rigid pusher element for pivotal movement into and out of theopen top of the magazine about an axis extending transverse to thedirection of the elongated path of movement of the pusher carriage,

and resilient means coupled to the pusher carriage to resiliently biasthe pusher carriage for movement toward the drive track.

9. The tool set forth in claim 8 in which the resilient means includesan extensible elongated flat spring means coupled between the toolhousing and the pusher carriage and disposed at the open end of themagazine housing overlying the fasteners on the fastener supportingstructure.

10. The tool set forth in claim 9 for use with U- shaped fasteners withspaced legs in which driver for driving generally U-shaped fastenerssuccessively supplied to a drive track,

a magazine housing communicating at one end with the drive track andhaving an open top,

a support disposed within the housing for supporting a strip of U-shapedfasteners,

a carriage slidably mounted on the housing adjacent its open end formovement toward and away from the drive track,

flat spring means connected between the tool and the carriage andoverlying the portion of the strip and the support that is disposedbetween the carriage and the drive track, said flat spring means biasingthe carriage toward the drive track,

pusher means with at least one rigid pusher arm piv' otally mounted onthe carriage for movement into and out of the open top of the housingand adapted to engage the U-shaped fasteners when disposed within themagazine housing, the flat spring means being provided with a clearanceto permit the pusher arm to move past the flat spring in moving into andout of the open end of the magazine housing and biasing means normallybiasing the pusher arm into the open top of the magazine housing to aposition for engaging a Ushaped fastener.

12. The tool set forth in claim ll in which the pusher means includes apair of rigid pusher arms connected for joint movement and normallydisposed within the magazine housing on opposite sides of the support,

said pair of pusher arms being spaced a given dis tance apart, and theflat spring means having a width less than said given distance .in theportion of the length of the flat spring means adjacent the pusher armso as to permit the pair of pusher arms to move into and out of the opentop of the magazine housing.

13. A: tool for driving fasteners comprising a housing having a cylindermeans closed at its lower end by a lower wall structure,

a power actuated drive means in the housing including a coupled pistonand driver blade movable within the cylinder means,

valve means for selectively connecting the cylinder means to pressurizedfluid to move the piston and driver blade through a power stroke,

a bumper on said lower wall structure and cooperating with the cylindermeans and the lower wall structure to provide a peripheral passagearound the bumper adjacent the lower wall structure communicating with aplurality of upwardly extending passages spaced circumferentially aroundthe outer surface of the bumper.

and means for supplying pressurized fluid to the peripheral passage tobe conveyed over said periprr era] and upwardly extending passages tothe interior of the cylinder means to move said piston and driver bladethrough a return stroke,

said means including a source of pressurized fluid and control meansresponsive to said drive stroke for interconnecting said source withsaid peripheral and upwardly extending passages.

14. A tool for driving fasteners into a workpiece comprising a housing.

a powered fastener driving assembly in said housing including a driverelement actuated by a drive piston slidablc within a movable drivecylinder,

fluid controlled main valve means opened to supply pressurized fluid toand closed to exhaust fluid from the cylinder to move the piston throughpower and return strokes.

said main valve means including passageways ex hausting said main valvemeans, and valve means movable to open and close said passageways,

said drive cylinder being movable with said passage way valve means, and

control means for controlling the main valve assembly, said controlmeans actuating said valve means to close said passageways prior tosupplying pres surized fluid to said cylinder to drive said piston andopening said passageways prior to the return stroke of said piston.

15. The tool set forth in claim l4 further comprising a lower wallstructure closing said cylinder at its lower end means for exhaustingthe portion of said housing be neath said drive piston, and said controlmeans controlling the movement of said cylinder from its closed positionwith said lower wall structure to an open position communicating saidcylinder with said exhaust means.

If). The tool set forth in claim 14 further comprising a bumper on saidlower wall structure cooperating with said cylinder and said lower wallstructure to provide a peripheral passage around the bumper adjacent thelower wall structure communicating with a plurality of upwardlyextending passages 23 24 spaced circumferentially around the outersurface blade through a return stroke, and of the bumper, said meansincluding a source of pressurized fluid means for supplying pressurizedfluid to the periphand control means responsive to said drive strokeera] passage to be conveyed over said peripheral for interconnectingsaid source with said peripheral and upwardly extending passages to theinterior of and upwardly extending passages.

I. l I! the cylinder means to move said piston and drive

1. A tool for driving fasteners into a workpiece comprising a poweredfastener driving assembly including a driver element actuated by a drivepiston slidable within a drive cylinder, a fluid controlled main valvemeans opened to supply pressurized fluid to and closed to exhaust fluidfrom the cylinder to move the piston through power and return strokes, acycle valve coupled to the main valve means and operable to alternatepositions to open and close the main valve means, said cycle valve beingbiased to a position to close the main valve means, said cycle valvealso including valve piston means, passage means coupling the valvepiston means to the drive cylinder to receive pressurized fluid forbiasing the cycle valve to a position to close the main valve means,return valve means responsive to the exhaust of the drive cylinder abovethe drive piston for supplying pressurized fluid into the drive cylinderbelow the drive piston to move the drive piston through a return stroke,the pressurized fluid below the drive piston being supplied to the valvepiston means to bias the cycle valve to a position to close the mainvalve means, and means responsive to the completion of the return strokeof the drive piston for controlling the return valve means to terminatethe supply of pressurized fluid to the drive cylinder below the pistonmeans and thus to the valve piston means.
 2. A tool as set forth inclaim 1 including a bias piston movable into engagement with the valvepiston means, and means coupling the bias piston to the return valvemeans to receive pressurized fluid from the return valve means.
 3. Atool as set forth in claim 1 including a valve seat adjacent the lowerend of the drive cylinder communicating with the atmosphere, and meansmovably mounting the drive cylinder for movement into engagement withthe valve seat when the main valve means is closed and out of engagementwith the valve seat when the main valve means is opened to exhaust thedrive cylinder below the piston.
 4. A tool as set forth in claim 3including port means in the cylinder forming a part of said passagemeans, said port means being opened to pressurized fluid in the drivecylinder above the drive piston when the cylinder is out of saidengagement with the valve seat and the drive piston is at the end of itspower stroke, said port means being closed by said drive piston when thedrive cylinder engages said valve seat and the drive piston is at theend of its power stroke.
 5. A tool for driving fasteners into aworkpiece comprising a housing, a cylinder slidably mounted in thehousing and slidably receiving a piston movable through power and returnstrokes, a fastener driving blade actuated by the piston, a main valvemeans opened to supply a pressurized fluid to the top of the cylinderand closed to exhaust fluid from the top of the cylinder, said mainvalve means including means engaging the cylinder to move the cylinderdown when the main valve means is closed and permitting upward movementof the cylinder when the main valve means is opened, a nosepiecestructure on the housing adjacent the lower end of the cylinder andhaving a drive track through which the fastener driving blade extends, acylindrical valve seat engaged by the lower end of the cylinder when themain valve means is closed and spaced below the lower end of thecylinder when the cylinder moves upwardly as the main valve means isopened, the space between the valve seat and the lower end of thecylinder exhausting the lower interior of the cylinder, a fluid actuatedcycle valve means coupled to the main valve means and automaticallyoperable through a sequence of two spaced positions to oPen and closethe main valve means, said cycle valve means including means responsiveto pressurized fluid from the lower end of the cylinder to effectclosure of the main valve means, a fluid controlled return valve meansresponsive to the closure of the main valve means for supplyingpressurized fluid to the cycle valve means to hold the main valve meansclosed and to the lower end of the cylinder below the piston to move thepiston through a return stroke, said fluid controlled return valve meansbeing released to terminate the supply of pressurized fluid when thepiston completes its return stroke, and control means for initiatingmovement of the cycle valve means to start a power stroke of the piston.6. A tool as set forth in claim 5 in which the cylindrical valve seat isfixedly secured to and projects upwardly from the nosepiece structure,and the return valve means is carried on the housing and includespassage means through the housing and nosepiece structure terminating ina discharge port disposed within the cylindrical valve seat.
 7. A toolfor driving fasteners into a workpiece comprising a housing defining achamber, a cylinder slidably mounted within the chamber for limitedmovement, a fluid actuated main valve assembly movable into and out ofengagement with the top portion of the cylinder, said cylinder beingfluid biased toward the main valve assembly and movable over a limitedtravel with the main valve assembly before separation of the top portionof the cylinder and the main valve assembly, a piston slidable withinthe cylinder, a fastener driving blade actuated by the piston, anosepiece structure on the housing adjacent the lower end of thecylinder and defining a drive track slidably receiving the fastenerdriving blade, an annular member fixedly secured to the nosepiecestructure encircling the fastener driving blade and aligned with thelower portion of the cylinder, a resilient sealing element carried onthe annular member adapted to be engaged by the lower portion of thecylinder when the main valve means is moved into engagement with the topof the cylinder to move the cylinder down into seating engagement withthe sealing element, said sealing element being spaced from the lowerportion of the cylinder when the main valve assembly is moved upwardlyout of engagement with the cylinder to permit limited upward movement ofthe cylinder away from the sealing element, a fluid passage passingthrough the housing and the nosepiece structure and having a port in thenosepiece structure within the annular member, and fluid control meanscoupled to the main valve assembly and to the fluid passage to move themain valve assembly into and out of engagement with the top portion ofthe cylinder and to supply fluid to the fluid passage.
 8. A tool fordriving fasteners comprising a tool housing with a nosepiece structureincluding a drive track, power actuated fastener driving means on thetool housing including a driver element movable in said drive track, amagazine housing with an open top coupled to the nosepiece structure andhaving a fastener supporting structure disposed below said open top forsupporting and feeding a series of fasteners into the drive track, apusher carriage mounted on said housing for movement toward and awayfrom the drive track along an elongated path, a rigid fastener engagingpusher element for engaging fasteners on said fastener supportingstructure, pivot structure coupling the pusher carriage and the pusherelement to mount the rigid pusher element for pivotal movement into andout of the open top of the magazine about an axis extending transverseto the direction of the elongated path of movement of the pushercarriage, and resilient means coupled to the pusher carriage toresiliently bias the pusher carriage for movement toward the drivetrack.
 9. The tool set forth in claim 8 in which the resilient meanSincludes an extensible elongated flat spring means coupled between thetool housing and the pusher carriage and disposed at the open end of themagazine housing overlying the fasteners on the fastener supportingstructure.
 10. The tool set forth in claim 9 for use with U-shapedfasteners with spaced legs in which a pair of rigid pusher elements arepivotally mounted on the pusher carriage and spaced from each other inthe direction of said axis to engage the spaced legs of the U-shapedfasteners, and the flat spring means includes a portion disposed betweenthe spaced pair of pusher legs.
 11. In a fastener driving tool having areciprocable driver for driving generally U-shaped fastenerssuccessively supplied to a drive track, a magazine housing communicatingat one end with the drive track and having an open top, a supportdisposed within the housing for supporting a strip of U-shapedfasteners, a carriage slidably mounted on the housing adjacent its openend for movement toward and away from the drive track, flat spring meansconnected between the tool and the carriage and overlying the portion ofthe strip and the support that is disposed between the carriage and thedrive track, said flat spring means biasing the carriage toward thedrive track, pusher means with at least one rigid pusher arm pivotallymounted on the carriage for movement into and out of the open top of thehousing and adapted to engage the U-shaped fasteners when disposedwithin the magazine housing, the flat spring means being provided with aclearance to permit the pusher arm to move past the flat spring inmoving into and out of the open end of the magazine housing, and biasingmeans normally biasing the pusher arm into the open top of the magazinehousing to a position for engaging a U-shaped fastener.
 12. The tool setforth in claim 11 in which the pusher means includes a pair of rigidpusher arms connected for joint movement and normally disposed withinthe magazine housing on opposite sides of the support, said pair ofpusher arms being spaced a given distance apart, and the flat springmeans having a width less than said given distance in the portion of thelength of the flat spring means adjacent the pusher arm so as to permitthe pair of pusher arms to move into and out of the open top of themagazine housing.
 13. A tool for driving fasteners comprising a housinghaving a cylinder means closed at its lower end by a lower wallstructure, a power actuated drive means in the housing including acoupled piston and driver blade movable within the cylinder means, valvemeans for selectively connecting the cylinder means to pressurized fluidto move the piston and driver blade through a power stroke, a bumper onsaid lower wall structure and cooperating with the cylinder means andthe lower wall structure to provide a peripheral passage around thebumper adjacent the lower wall structure communicating with a pluralityof upwardly extending passages spaced circumferentially around the outersurface of the bumper, and means for supplying pressurized fluid to theperipheral passage to be conveyed over said peripheral and upwardlyextending passages to the interior of the cylinder means to move saidpiston and driver blade through a return stroke, said means including asource of pressurized fluid and control means responsive to said drivestroke for interconnecting said source with said peripheral and upwardlyextending passages.
 14. A tool for driving fasteners into a workpiececomprising a housing, a powered fastener driving assembly in saidhousing including a driver element actuated by a drive piston slidablewithin a movable drive cylinder, fluid controlled main valve meansopened to supply pressurized fluid to and closed to exhaust fluid fromthe cylinder to move the piston through power and return strokes, saidmain valve means including passageways exhausTing said main valve means,and valve means movable to open and close said passageways, said drivecylinder being movable with said passageway valve means, and controlmeans for controlling the main valve assembly, said control meansactuating said valve means to close said passageways prior to supplyingpressurized fluid to said cylinder to drive said piston and opening saidpassageways prior to the return stroke of said piston.
 15. The tool setforth in claim 14 further comprising a lower wall structure closing saidcylinder at its lower end, means for exhausting the portion of saidhousing beneath said drive piston, and said control means controllingthe movement of said cylinder from its closed position with said lowerwall structure to an open position communicating said cylinder with saidexhaust means.
 16. The tool set forth in claim 14 further comprising abumper on said lower wall structure cooperating with said cylinder andsaid lower wall structure to provide a peripheral passage around thebumper adjacent the lower wall structure communicating with a pluralityof upwardly extending passages spaced circumferentially around the outersurface of the bumper, means for supplying pressurized fluid to theperipheral passage to be conveyed over said peripheral and upwardlyextending passages to the interior of the cylinder means to move saidpiston and drive blade through a return stroke, and said means includinga source of pressurized fluid and control means responsive to said drivestroke for interconnecting said source with said peripheral and upwardlyextending passages.